Build minimal requirements list with pipdeptree.

requirements.txt

@@ -1,27 +1,12 @@
 arrow==0.10.0
-certifi==2017.7.27.1
-chardet==3.0.4
-click==6.7
 dateutils==0.6.6
-Flask==0.12.2
 gunicorn==19.7.1
 HiYaPyCo==0.4.11
-idna==2.6
-isodate==0.5.4
-itsdangerous==0.24
-Jinja2==2.9.6
-MarkupSafe==1.0
 numpy==1.13.3
-py==1.4.34
-pyparsing==2.2.0
-pytest==3.2.2
-python-dateutil==2.6.1
-pytz==2017.2
-PyYAML==3.12
-rdflib==5.0.0.dev0
-requests==2.18.4
+Pillow==4.3.0
+pipdeptree==0.10.1
+pytest-flask==0.10.0
 requests-toolbelt==0.8.0
-six==1.10.0
 SPARQLWrapper==1.8.0
-urllib3==1.22
-Werkzeug==0.12.2
+wheel==0.30.0a0
+